Three-dimensional numerical models were used to determine the permeable pathways between the HANDLEY underground nuclear test and downgradient boreholes ER-20-12 and PM-3, Pahute Mesa, southern Nevada. The SEAWAT code was used to couple MODFLOW and MT3DMS models, where the coupled model simulated groundwater-flow and tritium migration from the HANDLEY test for 50 years, from the date of detonation of the HANDLEY test (March 26, 1970) to March 26, 2020. Recharge, hydraulic-conductivity, specific-storage, and effective-porosity distributions were estimated using parameter estimation (PEST) by minimizing a weighted composite, sum-of-squares objective function. Simulated water-level altitudes in 10 wells, vertical water-level differences between 5 well pairs, aquifer-test transmissivity estimates in 9 wells, tritium concentrations in 7 wells, and drawdowns in wells PM-3-1 and PM-3-2 from groundwater withdrawals in borehole ER-20-12 were compared to measured equivalents during parameter estimation and formally defined the goodness-of-fit or improvement of calibration. This USGS data release contains data, analyses, and model files for the simulations and analyses described in the associated model documentation report (https://doi.org/10.3133/sir20215032).

Supplementary data and analyses are in the ancillary directory, including transmissivity estimates (Appendix A); water-level models to estimate drawdowns (Appendix B); tritium data (Appendix C); the modified hydrostratigraphic framework in the numerical models (Appendix D); effective-porosity estimates (Appendix E); the Pahute Mesa–Oasis Valley groundwater model (Appendix F); model-calibration files (Appendix G); and pre-processing routines to build model files (Appendix H).

The numerical model was calibrated using a multi-model approach and a two-step process. First, the groundwater model was calibrated, which consists of (1) a steady-state model simulating steady-state (predevelopment) groundwater flow; and (2) a transient model simulating drawdowns from groundwater withdrawals during the drilling of borehole ER-20-12. A transport model was developed that uses the best-fit estimated hydraulic-conductivity field from the calibrated groundwater model and was used to estimate dispersion and effective porosities.